The present invention relates in general to elevator operating mechanisms and in particular to an improved power supply and drive system for an elevator.
Many elevator power supply and drive systems are known in the art. Such systems are adapted to selectively rotate a cylindrical drum upon which an elevator car and counterweight are suspended by cables. Typically, a Ward Leonard system is provided having a generator driving a hoist motor which rotates the drum. An electric motor is normally connected to a power source for the building in which the elevator is located in order to drive the generator. Additionally, in most buildings, an emergency generator is provided as a back-up power source for the electric motor in case of a power failure in the building.
One problem encountered in the design of such elevator systems is that both the electric motor for driving the Ward Leonard generator and the emergency generator must have sufficient capacity to fulfill both the average power requirement of the elevator system during normal operation and the instantaneous power surge requirements encountered during use. Unfortunately, the cost of constructing large electric motors and generators capable of handling these power surge requirements is quite high. It is also inefficient to utilize such large electric motors and emergency generators, since their full capacity is only infrequently needed. Accordingly, it would be desirable to provide a power supply and drive system for an elevator which generates a steady flow of power representing the integrated requirement of the elevator over its prolonged duty period, yet is capable of handling relatively high instantaneous power surge requirements.